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That coveted bowl of shark fin soup, those shark cartilage capsules said to bring health benefits, might not only be bad for the oceans but also pose a risk for degenerative brain disease in humans.

A new study from University of Miami researchers shows shark fin contains high concentrations of a neurotoxin linked to neurodegenerative diseases including Alzheimer’s and Lou Gehrig’s disease (also Amyotrophic lateral sclerosis, ALS).

The findings, published in the journal Marine Drugs, followed the testing of seven species of shark: blacknose, blacktip, bonnethead, bull, great hammerhead, lemon, and nurse sharks for β-N-Methylamino-L-alanine, or BMAA. Samples were collected as fin clips from live shark in South Florida waters.

The study’s co-author, Professor Deborah Mash, director of the University of Miami Brain Endowment Bank, was part of a 2009 study that showed patients diagnosed with Alzheimer’s Disease and ALS had unusually high levels of BMAA in their brains of up to 256 ng/mg. By contrast, healthy people, the study showed, had no BMAA, or only trace quantities of the toxin in their bodies.

In this latest study, the team found high BMAA levels of between 144 and 1836 ng/mg in shark fins.

BMAA is produced by cyanobacteria, which are found in lakes, rivers, estuaries, and marine waters where nutrient loading from agricultural and industrial runoff, sewage, groundwater inflow and atmospheric pollution accelerate bloom growth.

This is then eaten by small aquatic marine animals, which in turn are consumed by sharks, potentially posing a health risk to consumers of shark products.

The study cautioned that, “further studies are needed to confirm this finding and to demonstrate that widespread BMAA detections in sharks may occur outside of South Florida coastal waters.”

High concentrations of BMAA were, however, detected in the fins of some sharks collected in areas with no active cyanobacteria blooms. Sharks are highly migratory, making it likely that they pass in and out of areas where cyanoblooms may have occurred over time, the study says.

Consumers in Asia eat shark fin soup at wedding or official banquets and purchase shark fin cartilage powder or capsules as dietary supplements, which claim to combat and/or prevent a variety of illnesses.

However, the study points out that, “the benefits of these supplements have not been significantly proven, nor has shark cartilage been reviewed by the US Food and Drug Administration.

Let’s hope regular consumers of shark products think carefully about their health before slurping down another bowl of shark fin soup or popping more cartilage capsules.